Figures (7)

Rotational state populations ρmjj vs. j of HCN gas for selected m-values (a) before illumination (thermal population), (b) after illumination by a 15TW/cm2, 100fs, 800nm optical alignment pulse, and (c) after a train of four such pulses separated by 11.49ps (the revival time of HCN). Below are intensity plots of ρmjj vs. j and m for (d) thermal, (e) one-pulse, and (f) four-pulse illumination.

A 1TW/cm2 optical pulse weakly aligns HCN and strongly modulates (a) terahertz energy absorbed/emitted per molecule, per m=0,j→j-1 transition depending on the optical-terahertz relative delay ΔT. (b) Averaging over delay shows the ‘incoherent’ absorption that a terahertz pulse would experience if it was not collinear with the optical pump pulses. (c) Summing over j gives total absorption vs. ΔT.